U.S. patent application number 10/678026 was filed with the patent office on 2004-04-01 for method of self-aligning optical waveguides.
Invention is credited to Johannessen, Kjetil.
Application Number | 20040060324 10/678026 |
Document ID | / |
Family ID | 21914245 |
Filed Date | 2004-04-01 |
United States Patent
Application |
20040060324 |
Kind Code |
A1 |
Johannessen, Kjetil |
April 1, 2004 |
Method of self-aligning optical waveguides
Abstract
A first waveguide and a second waveguide are aligned by applying
an alignment dot on end surfaces of the cores of first and second
waveguides. The alignment dots are positioned in close proximity to
one another, and are melted together. Surface tension pulls the
first and second waveguides into alignment.
Inventors: |
Johannessen, Kjetil;
(Trondheim, NO) |
Correspondence
Address: |
Charles K. Young
BLAKELY, SOKOLOFF, TAYLOR & ZAFMAN LLP
Seventh Floor
12400 Wilshire Boulevard
Los Angeles
CA
90025-1030
US
|
Family ID: |
21914245 |
Appl. No.: |
10/678026 |
Filed: |
September 30, 2003 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10678026 |
Sep 30, 2003 |
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10041014 |
Dec 28, 2001 |
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6684015 |
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Current U.S.
Class: |
65/386 ;
65/395 |
Current CPC
Class: |
G02B 6/2551 20130101;
G02B 6/30 20130101; G02B 6/4203 20130101; G02B 6/34 20130101; G02B
6/13 20130101 |
Class at
Publication: |
065/386 ;
065/395 |
International
Class: |
C03B 037/15 |
Claims
What is claimed is:
1. A method of aligning a first waveguide and a second waveguide,
the first and second waveguides each having a core, the first and
second waveguides comprised of dissimilar materials, the method
comprising: applying a first alignment dot to an end surface of the
core of the first waveguide; applying a second alignment dot to an
end surface of the core of the second waveguide; positioning the
first alignment dot in proximity to the second alignment dot; and
melting the first and second alignment dots together.
2. The method of claim 1, wherein the first waveguide is an optical
fiber.
3. The method of claim 1, wherein the second waveguide is a planar
waveguide.
4. The method of claim 1, wherein applying the first alignment dot
to an end surface of the core of the first waveguide further
comprises: applying a photo sensitive optical material to an end
surface of the first waveguide; exposing the photo sensitive
optical material to a light beam traveling through the core of the
first waveguide, the light beam having a wavelength that cures the
photo sensitive optical material to create a first portion of the
photo sensitive optical material that is cured and a second portion
of the photo sensitive optical material that is not cured; removing
the second portion of the photo sensitive optical material that is
not cured.
5. The method of claim 4, wherein removing the second portion of
the photo sensitive optical material that is not cured further
comprises: using a solvent to remove the second portion of the
photo sensitive optical material that is not cured.
6. The method of claim 4, wherein removing the second portion of
the photo sensitive optical material that is not cured further
comprises: using an etch to remove the second portion of the photo
sensitive optical material that is not cured.
7. The method of claim 1, wherein applying the first alignment dot
to an end surface of the core of the first waveguide further
comprises: applying a mask to an end surface of the first
waveguide; ablating a portion of the mask by exposing the mask to a
high energy light beam traveling through the core of the first
waveguide to create a mask opening; and filling the mask opening
with an optical material to form the first alignment dot.
8. The method of claim 7 further comprising: removing the mask from
the end surface of the first waveguide.
9. The method of claim 1, wherein the first alignment dot comprises
a polymer, a sol-gel, or a glass.
10. The method of claim 1 further comprising: using alignment dots
to align an array of optical waveguides.
11. A method of aligning an optical fiber to a planar waveguide,
the optical fiber and the planar waveguide each having a core, the
method comprising: applying a first alignment dot to an end surface
of the core of the optical fiber; applying a second alignment dot
to an end surface of the core of the planar waveguide; coupling the
first alignment dot to the second alignment dot; and melting the
first and second alignment dots together.
12. The method of claim 11 further comprising: allowing the optical
fiber or the planar waveguide to move while melting the first and
second alignment dots together.
13. The method of claim 12 further comprising: applying an
additional bonding agent between or around the optical fiber and
the planar waveguide.
14. The method of claim 11, wherein the first alignment dot
comprises a polymer, a sol-gel, or a glass.
15. The method of claim 11, wherein the second alignment dot
comprises a polymer, a sol-gel, or a glass.
16. A method of aligning a first waveguide and a second waveguide,
the first waveguide having a core, the core of the first waveguide
having a first alignment dot attached to it, the second waveguides
having a core, the core of the second waveguide having a second
alignment dot attached to it, the first and second waveguides
having different cross-sectional shapes, the method comprising:
positioning the first alignment dot in proximity to the second
alignment dot; and melting the first and second alignment dots
together.
17. The method of claim 16 further comprising: allowing the first
waveguide or the second waveguide to move while melting the first
and second alignment dots together.
18. The method of claim 17 further comprising: applying a bonding
agent over the first and second alignment dots to better adhere the
first and second waveguides together.
19. The method of claim 17 further comprising: applying a curable
polymer over the first and second alignment dots to better adhere
the first and second waveguides together.
20. The method of claim 17 further comprising: using alignment dots
to align multiple waveguides at substantially the same time.
21. The method of claim 20 further comprising: using the alignment
dots to align a fiber ribbon.
22. A method of forming a self-aligning alignment dot on an end
surface of a waveguide, the method comprising: applying a mask to
an end surface of the waveguide; ablating a portion of the mask by
exposing the mask to a high energy light beam traveling through the
waveguide to create a mask opening; and filling the mask opening
with an optical material.
23. The method of claim 22 further comprising: removing the mask
from the end surface of the waveguide.
24. The method of claim 22, wherein ablating a portion of the mask
further comprises: ablating the portion of the mask with an
ablating light.
25. The method of claim 24 further comprising: coupling an optical
probe to the waveguide to provide the ablating light.
26. The method of claim 25 further comprising: positioning the
optical probe in a probe region above the waveguide, the probe
region having a waveguide upper cladding that has been at least
partially removed.
27. The method of claim 25 further comprising: positioning the
optical probe in a probe region above the waveguide, the probe
region having an upper cladding of approximately 0-3 microns.
28. The method of claim 25, wherein the ablating light is an UV
light.
29. The method of claim 22, wherein the waveguide is an optical
fiber.
30. The method of claim 29 further comprising: aligning a far end
of the optical fiber to a light source; forming the self-aligning
alignment dot on an opposite end of the optical fiber; cutting off
a segment of optical fiber with the self-aligning alignment dot;
and forming another self-aligning alignment dot on the opposite end
of the optical fiber without re-aligning the far end of the optical
fiber.
31. The method of claim 22, wherein the waveguide is a planar
waveguide.
32. The method of claim 22, wherein the optical material comprises
a polymer or a sol-gel.
33. A method of forming a self-aligning alignment dot on an end
surface of a waveguide, the method comprising: applying a photo
sensitive optical material to an end surface of the waveguide;
exposing the photo sensitive optical material to a light beam
traveling through the waveguide, the light beam having a wavelength
that cures the photo sensitive optical material to create a cured
portion of the photo sensitive optical material and an uncured
portion of the photo sensitive optical material; and removing the
uncured portion of the photo sensitive optical material.
34. The method of claim 33, wherein removing the uncured portion of
the photo sensitive optical material further comprises: using a
solvent to remove the uncured portion of the photo sensitive
optical material.
35. The method of claim 34, wherein removing the uncured portion of
the photo sensitive optical material further comprises: using an
etch to remove the uncured portion of the photo sensitive optical
material.
36. The method of claim 33 further comprising: coupling an optical
probe to the waveguide to provide the light beam traveling through
the waveguide.
37. The method of claim 33, wherein the waveguide is an optical
fiber.
38. The method of claim 37 further comprising: aligning a far end
of the optical fiber to a light source; forming the self-aligning
alignment dot on an opposite end of the optical fiber; cutting off
a segment of optical fiber with the self-aligning alignment dot;
and forming another self-aligning alignment dot on the opposite end
of the optical fiber without re-aligning the far end of the optical
fiber.
39. The method of claim 37, wherein the waveguide is a planar
waveguide.
40. The method of claim 33, wherein the photo sensitive optical
material comprises a polymer or a sol-gel.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The described invention relates to the field of optical
circuits. In particular, the invention relates to a method of
self-aligning optical waveguides.
[0003] 2. Description of Related Art
[0004] Aligning optical waveguides can be difficult. If the
waveguides are the same, such as two optical fibers, they can be
fused together without too much difficulty. However, if the
waveguides are made from dissimilar materials, or have different
cross-sectional shapes, it is more difficult to align the
waveguides.
BRIEF DESCRIPTION OF THE DRAWINGS
[0005] FIG. 1 is a schematic diagram showing a cross-sectional view
of two waveguides being aligned using alignment dots.
[0006] FIG. 2 is a schematic diagram showing a cross-sectional view
of the two waveguides after being aligned by heating the alignment
dots that have melted together.
[0007] FIGS. 3A-3D are schematic diagrams showing the process of
applying an alignment dot to a waveguide.
[0008] FIGS. 4A-4E are schematic diagrams showing an alternate
embodiment of applying an alignment dot to a waveguide having a
core.
[0009] FIG. 5 is a flowchart showing one embodiment of applying an
alignment dot comprising glass.
DETAILED DESCRIPTION
[0010] A method of self-aligning two waveguides is described. A
first waveguide and a second waveguide are aligned by applying an
"alignment dot," i.e., a small portion of optical material, e.g., a
thermal polymer, on the end surfaces of the cores of first and
second waveguides. The alignment dots are positioned in close
proximity to one another, and are melted together. Surface tension
pulls the first and second waveguides into alignment. The method
may be used for waveguides having dissimilar cross-sectional
shapes, or for waveguide comprising dissimilar materials. In one
embodiment, an optical fiber is aligned to a planar waveguide. The
method may be employed for aligning multiple waveguides at the same
time, such as in aligning an optical fiber ribbon with a planar
lightwave circuit.
[0011] FIG. 1 is a schematic diagram showing a cross-sectional view
of two waveguides being aligned using alignment dots. In one
embodiment, the first waveguide is a planar waveguide 10, and the
second waveguide is an optical fiber 20. The planar waveguide
comprises an upper cladding 12, a lower cladding 14 and a core 16.
An alignment dot 30 has been applied to the end surface of the core
16 of the planar waveguide 10, as will be described in more detail
with respect to FIGS. 3A-3D and 4A-4E.
[0012] The optical fiber 20 comprises an outer cladding 22 and a
core 24. An alignment dot 40 has been applied to an end surface of
the core 24 of the optical fiber 20, as will be described in more
detail with respect to FIGS. 3A-3D and 4A-4E.
[0013] In order to align the planar waveguide 10 with the optical
fiber 20, their alignment dots 30, 40 are placed in close proximity
with one another. The alignment dots are then heated until they
melt together. At least one of the waveguides 10, 20 is allowed to
move as the alignment dots melt, and the surface tension of the
alignment dots pulls the waveguides 10, 20 into alignment with one
another.
[0014] FIG. 2 is a schematic diagram showing a cross-sectional view
of the two waveguides 10, 20 after being aligned by heating the
alignment dots 80 that have been melted together. In one
embodiment, a bonding agent 82 is applied between and/or around the
two waveguides 10, 20 to strengthen the bond between the two
waveguides 10, 20 and prevent them from subsequently shifting and
becoming mis-aligned.
[0015] FIGS. 3A-3D are schematic diagrams showing the process of
applying an alignment dot to a waveguide 100. FIG. 3A is a
cross-sectional view of a waveguide 100 having a core 102. The
process of applying the alignment dot is substantially the same
whether the waveguide 100 is an optical fiber or a planar
waveguide.
[0016] FIG. 3B is a schematic diagram that shows a photo sensitive
polymer layer 110 applied to an end surface of the waveguide 100.
The photo sensitive polymer layer may be applied by any of various
deposition techniques. For example, in one embodiment, the photo
sensitive polymer layer is spin coated on the end surface of the
waveguide 100. In another embodiment, the waveguide 100 is coated
by dipping it into the photo sensitive polymer.
[0017] FIG. 3C shows the polymer layer 110 being exposed to a light
beam 120 traveling through the waveguide 100. A portion 130 of the
photo sensitive polymer is cured by the light beam. In one
embodiment, the light beam is of an ultraviolet (UV) wavelength.
Alternatively the light beam may be in the visible spectrum, e.g,
of approximately 630 nm or shorter. However, the polymer can be
selected to be cured by other wavelengths.
[0018] FIG. 3D shows the cured portion 130 of the polymer layer 110
after the uncured portion of the polymer layer 110 has been
removed. The uncured portion of polymer may be removed by using a
solvent or an etch. The cured portion 130 is the alignment dot.
[0019] FIGS. 4A-4E are schematic diagrams showing an alternate
embodiment of applying an alignment dot to a waveguide 200 having a
core 202. FIG. 4A is a cross-sectional view of a waveguide 200
after a masking layer 210 has been applied to the end surface of
the waveguide 200. In one embodiment, the masking layer comprises a
polymer.
[0020] FIG. 4B shows the masking layer 210 of polymer being exposed
to a light beam 220 traveling through the waveguide 200. The light
beam 220 is a high energy light beam that causes ablation of an
area 222 of the masking polymer 210 in the guided mode of the
waveguide 200.
[0021] FIG. 4C shows the waveguide 200 and masking layer 210 after
the ablation is complete. A mask opening 230 has been created by
the ablation.
[0022] FIG. 4D shows the mask opening 230 filled with an optical
material, such as a thermal polymer 240. This can be accomplished
by various methods. In one embodiment, a small amount of polymer
material is placed in the opening 230 and around the opening. The
material is melted and allowed to enter into the opening 230. The
resulting dot may be larger than the thickness of the masking
layer. In some cases, the resulting dot may be significantly larger
than the thickness of the masking layer. In another embodiment, the
whole end surface of the waveguide 200 is covered with the thermal
polymer, e.g., by dip-coating, and the thermal polymer fills up the
opening 230.
[0023] FIG. 4E shows the thermal polymer 240 after the masking
layer 210 has been removed, e.g., by an etch or a solvent. The
alignment dot has been formed. Depending on the thickness of the
masking layer 210 and the thickness of the thermal polymer 240, the
masking layer 210 may optionally be left on the end surface of the
waveguide.
[0024] With respect to the photo ablation method of FIGS. 4A-4E, in
one embodiment, the end surface of the waveguide may be chemically
treated, e.g., with silane or hydrofluoric acid, to modify the
characteristics of the surface to allow the polymer to form a small
drop. After both the photo curing and the photo ablation processes,
the waveguide may be pre-baked to improve adhesion of the alignment
dot to the end surface of the waveguide.
[0025] In both the photo curing method (FIGS. 3A-3D) and the photo
ablation method (FIGS. 4A-4E), a light beam was directed through
the waveguide. Returning to FIG. 1, one way of transmitting a light
beam into the core 16 of the planar waveguide 10 is by coupling an
optical probe 60 to the waveguide 10. In one embodiment, a portion
of the upper cladding 12 of the waveguide 10 is removed so that the
optical probe 60 may be coupled to the waveguide with less than
approximately 3 microns of cladding. For example, the upper
cladding of the planar waveguide may be selectively etched off over
the waveguide 10. Alternatively, the optical probe 60 may be
coupled to a planar waveguide that either has no upper cladding or
has only a very thin upper cladding. Additionally, an index-matched
fluid may be used to better couple the optical probe 60 to the
planar waveguide 10. The angle of the probe, its refractive index,
and the angle of light input to the probe allow selection of the
fundamental mode within the waveguide 10.
[0026] In one embodiment, an UV light is used for the photo curing
and photo ablation methods. One problem with using a UV light
guided through the planar waveguide 10, is that the planar
waveguide 10 has a very high loss for short wavelengths. However,
by using the optical probe close to an edge of the planar
waveguide, e.g., less than a millimeter from the edge, a strong UV
light beam can be transferred from the optical probe to the
waveguide and emitted from the waveguide for use in the previously
described photo curing and photo ablation methods. Using a high
power light source with the optical probe also provides the
advantage of allowing relatively easy alignment of the optical
probe to the planar waveguide 10.
[0027] Light for the photo curing and photo ablation methods may
also be provided via the optical fiber upon which an alignment dot
is placed. In one embodiment, multiple optical fibers may be
optically coupled to a common light source. This allows alignment
dots to be applied to multiple optical fibers at the same time.
[0028] Precise alignment of the optical fiber to the light source
is very important to primarily exciting the fundamental mode in the
optical fiber. A single mode optical fiber (e.g., at 1550 nm) may
be cured or ablated with a light source (e.g., of 630 nm) at a far
end of a long (e.g., 100 m) optical fiber. Precise alignment of the
optical fiber to the light source may be time consuming; however,
this alignment need only be done once. Alignment dots may be
sequentially applied to the opposite end of the optical fiber with
each of the optical fibers (having an alignment dot) being cut to
the desired fiber length.
[0029] Although the previous discussion has been focused on using a
thermal polymer for the alignment dots, other materials may
alternatively be used. For example, a glass or SOL-GEL may be used
as alignment dots. In particular, a low melting temperature glass
has a high affinity for other glasses, and may be used for coupling
and aligning a silica waveguide to an optical fiber, for
example.
[0030] FIG. 5 is a flowchart showing one embodiment of applying an
alignment dot comprising glass. The flowcharts starts at block 300,
and continues with block 310, at which a mask is applied to the end
surface of a waveguide. In one embodiment, a polymer is used as the
mask.
[0031] From block 310, the flowchart continues at block 320, at
which the mask is ablated by a light source, such as a UV light
source. At block 330, a glass having a low temperature melting
point is applied over the ablation area. In one case, the glass has
a melting point of approximately 600.degree. C., and sputtering is
used to apply the low temperature melting point glass.
[0032] From block 330, the flowchart continues at block 340, at
which the glass is heated. In one embodiment, the glass is slowly
heated to approximately 650.degree. C. The mask polymer decomposes
around 200.degree. C. to 300.degree. C., leaving the glass in the
ablation area. The glass melts around 600.degree. C. As the glass
melts, it forms a drop. In one case, the decomposed polymer leaves
carbon debris over the end surface of the waveguide except at the
ablased opening, which assists at centering the glass drop to the
ablased area. The flowchart ends at block 350.
[0033] Thus, a method of self-aligning two waveguides is disclosed.
However, the specific embodiments and methods described herein are
merely illustrative. For example, the described methods are easily
extendable to aligning multiple waveguides, such as in a fiber
ribbon, to multiple waveguides in a planar lightwave circuit.
Numerous modifications in form and detail may be made without
departing from the scope of the invention as claimed below. The
invention is limited only by the scope of the appended claims.
* * * * *